The invention relates generally to locomotive air compressors and aftercoolers used to substantially reduce the temperature of high pressure air exiting the compressor, and particularly to a means for preventing downstream freezing of condensate in the high pressure air when outside ambient conditions are at or below freezing.
U.S. Pat. No. 5,106,270 to Goettel et al., and assigned to the assignee of the present invention, shows an integral compressor and aftercooler that is extremely efficient in cooling hot, high pressure discharge air from a compressor. When the compressor is operating under a heavy duty cycle the air temperature is reduced to within 2xc2x0 of ambient temperature. If the compressor is running in a start/stop manner under a light duty cycle, the temperatures of the heated gases from the compressor can be reduced to temperatures within 5xc2x0 of ambient. With such efficiency it is quite possible for moisture contained in the aftercooler or in the discharge air from the aftercooler to freeze when operating under freezing conditions.
The present invention provides a means to increase airstream temperatures flowing from an aftercooler to essentially remove the possibility of freezing prior to reaching a reservoir of pressurized air or bypass the aftercooler altogether should freezing occur in the aftercooler. The reservoir is typically fitted with a heated drain valve that removes (drains) condensate from the reservoir. The freezing problem is solved by bypassing the aftercooler with at least a portion of the hot air issuing from the compressor and directing the hot air to exhaust piping of the aftercooler. If the aftercooler freezes, all hot air is bypassed. In either case, warm air is supplied to the reservoir.
In one embodiment of the invention, by-pass of the aftercooler can be effected by a pipe connected between the compressor and aftercooler exhaust. The pipe provides a constant volume of hot, compressed air flow from the compressor to the aftercooler exhaust.
In another embodiment of the invention, a three-way valve is used to mix gases exhausting from the high pressure head of the air compressor and from an aftercooler to provide the warmer airstream. In both embodiments, condensate is prevented from freezing in the aftercooler exhaust and thus remains in liquid form long enough to reach the reservoir and the heated drain valve.
The three-way valve can be operated by sensing either the main reservoir inlet temperature or more simply ambient air temperature. Thus, in nonfreezing conditions, the three-way valve directs all high pressure air through the aftercooler so that it can be cooled and any moisture therein condensed. If, on the other hand ambient temperature falls below a certain level, the three-way valve is operated by temperature sensing means to bypass at least a portion of the high pressure air leaving the compressor.
It is, therefore, one of the primary objects of the present invention to provide a method and an apparatus to prevent freezing of condensate in high pressure air before it reaches a main reservoir in a locomotive and train braking system.
Another object of the present invention is to provide a method and an apparatus which provides a constant low volume flow of hot exhaust gases from a compressor directly to aftercooler exhaust piping, the aftercooler being connected to receive the major portion of hot gases from the compressor for cooling.
Yet another object of the present invention is to provide a method and an apparatus using a three-way valve that is effective in bypassing an aftercooler when freezing temperatures are sensed.
In addition to the various objects and advantage of the invention described above, various additional objects and advantages of the invention will become more readily apparent to those persons skilled in the pneumatic art from the following more detailed description of the invention, particularly, when such description is taken in conjunction with the attached drawing Figures and the appended claims.